1. Field of the Invention
The invention in general relates to semiconductor epitaxial layer growth, and more particularly to a ceiling for a growth reactor capable of growing silicon carbide semiconductors layers.
2. Description of Related Art
Silicon carbide is being used extensively as a semiconductor material for various electronic applications. Silicon carbide is a wide bandgap semiconductor with desirable material properties including high breakdown field strength 10 times larger, and thermal conductivity 3 times larger than conventional semiconductor materials. Accordingly, semiconductor devices of silicon carbide have the ability to operate at higher voltages and temperatures than conventional silicon or gallium arsenide devices thus providing for higher power devices with reduced cooling requirements that operate from dc to microwave frequencies.
Electronic applications for silicon carbide semiconductor devices include compact, low cost airborne, ship and ground radars, aircraft engine and flight controls, electric tank and ship propulsion systems and satellite communications, to name a few. In the commercial sector, silicon carbide may be used in the field of high definition television, industrial power conditioning, nuclear control and instrumentation and electric vehicle power trains.
In one popular process for the fabrication of a silicon carbide semiconductor device, thin epitaxial layers of silicon carbide are deposited by an epitaxial technique known as vapor phase epitaxy, a special case of the more general chemical vapor deposition. In vapor phase epitaxy the crystal structure and polytype of a relatively thick substrate is reproduced, but with higher purity and crystalline quality than the substrate. In addition, intentional impurity atoms of a dopant are added as desired to produce numerous layers with tailored conductivity and carrier type.
The epitaxial layers are grown in a device known as a reactor. In one well known type of reactor used for growing epitaxial layers of III-V compounds, such as gallium arsenide, a plurality of wafer substrates may be accommodated by a graphite susceptor located below a ceiling member having a central aperture through which various gases are supplied by a nozzle. The wafers are rotated as the susceptor is rotated during the deposition process. Typical reactor temperature during epitaxial deposition is approximately 800.degree. C. for the III-V compounds and 1200.degree. C. for silicon. To grow epitaxial layers of silicon carbide, however, requires much higher temperatures, in the range of 1450-1700.degree. C., and at these temperatures conventional reactor ceilings tend to adversely affect the growth process or even catastrophically fail.
The present invention provides for a ceiling design that will allow for III-V compounds or silicon epitaxial growth as well as higher temperature silicon carbide epitaxial growth.